Triple-modulation directive radio beacon system



June 13, 1933. H. DIAMOND ET AL TRIPLE MODULATION DIRECTIVE RADIO BEACON SYSTM Filed March 9, 1932 2 Sheets-Sheet l ALvN A|N l l I l I l I l l I l I I l ILIIII- LION wuantofd June 13, 1933. H. DIAMOND ET AL 1*,91398 TRIPLE MODULATION DIRECTIVE RADIO BEACON SYSTEM Filed March 9, 1932 2-Sheets-Sheet 2 FlGURE Z RESULTANT CARRJER 50 sms BAND y uur. 'ro w,

SIUE BAND n u E. `ro w3 FIURE. 3

REED AMvm-ruba FIGURE. 4

Quito: ne 14 5i) transmitted only during approximately one-V Patented June 13, 1933 UNiTED STATES isiaai PATENT. Fris HARRY DIAMOND, OF WASHINGTON, DISTRICT COLUMBIA, ANI)` FRANK G. KEAR, OF IVIINERSVILLE, PENNSYLVANIA, ASSIGi-NGRS TO` THEGO'VERNMENT OF THE UNITED STATES, AS REPRESENTED BY THE SECRETARY V0F COMMERCE TRIPLE-MODULATION DIRECTIVE RADIO :BEACON SYSTEM Application filed March 9, 1932. Serial No. 597,756.

j (GRANTED UNDER Tini ACT or MARCH syiasaas AMENDEDAPRIL 3o, 1928; 37o o. e. 757) The invention described herein may be manufactured and used by or for the Grov-y ernment of the United States for governmental purposes only without the paymentV of: any royalty thereon. Y -z The invention relates to improvements in the methodand apparatus for producing directive radio beacon signals, utilizing a single transmitter and antenna system, capable of serving more than four courses simultaneously. Y

VAnother object of our invention is to provide means for aligning the beaconcourses to the airways.

In a copending application of Harry Dia-f mond, Serial No. 597,757,iled March 9, 1932, for U. S. patent, the triple-modulation di rective radio beacon is V4described and shown to yield twelve useful courses normally dise posed 30 degrees from each other. Methods for shifting thecourses to4 align them to the airways are also described. T he invention herein described utilizes certain ofthe desirable features of the invention set forth in the application referred to, :to-

gether with othernovel features whereby fur.- Y

' fold: (a) a decided increase in the ther desirable results are secured. -V Y The transmitting system disclosed in the application referred to involves inefficient and cumbersome equipment diiicult toV adjust and involving considerable loss of power, asV

for example, the use of link circuitsto eliminate coupling between stator windings and the need for supplying an auxiliary carrier to replace the one suppressed by the goniomf eter systems. rlhese circuits are critical .in their adjustment since satisfactory results ca n only be obtained when the vertical antenna is in accurate phase adjustment with respect toV A the beacon carrier frequency.

The substitution of means for exciting but one stator winding at a time simplifies the circuits but withV an attendant loss of power. The net power transmitted by each amplifier branch,when using a grid-biasing arrangef ment for switching radio-frequency supply successively to each amplifier train at Van audio-frequency rate, is reduced considerably below the normal; primarily because power is `the tube characteristic from the point of cutoff to the point'of normal operation and back to the cut-0E point.

@ur purpose is to simplify the apparatusv and render it more efficient for use at the junction of a large number .of airways, capable of serving from one to twelve air routes simultaneously.

rlhe use of S-phase audio-frequency for switching the radio-frequency power as described above suggestedthat the same results could be obtained if a source of B-phase radiofrequency were available. Each phase of this S-phase radio-frequencysupply could then-be used for supplying carrier voltage to the grid of one intermediate amplifier, the S-phase source thus servingv as a master oscillator as well as a switching device.

A circuit accomplishing the desired object was constructed and will be described hereinafter with the results obtained.

As will appear from the following descrip'- tion, the advantages to be gained lthrong-gh the use of radio frequency switching are fouiower transmitted by each ampler branch; (l the elimination of a three-phase audio-frequency unit or of anti-coupling devices; (c) the operation of the intermediate amplifier tubes under normal conditions land not with the high grid voltages necessary in the method of grid-bias switching; and (d) the elimination of interference caused by the audio-frequency used for grid biasing. l

Referring to the drawings, Figure l is a schematic diagram of the transmitter and antenna system of the triple-modulation directive radio beacon, using the method of radio frequency switching embodying our in-rv vention;

. Figurefl shows the voltage vector diagram forthe three-phase radio-.frequency master oscillator arrangement employed in Figure l.

VFigure 3 .shows the beacon space pattern when using B-phase radio-frequencyv switch ing.

Vrent to the amplifier tubes.

form of master oscillatorl which produces aV continuous wave carrier, which is connected for supplying radio-frequency voltage in equal proportions to the control grids of the three intermediate amplifier tubes 12, 13 and V14. Two conductors are connected to the oscillator at the points 15 and 16 for the purpose of conducting the radio-frequency cur- Advantage is taken ofthe fact that the voltages .at these two points to ground are approximately 180 degrees out of time phase. A non-inductive resistor 17 and a capacitor 18 are inserted in series with one conductor to advance the time-phase of its radio-frequency current in order to compensate for the eH-ect of load upon the 180 degrees phase difference between the two points 15and 16. through the adjustabler capacitor 18, the current is again divided at 19 into two branches,

some passing through a non-inductive resistor 20 and an inductor 21 to the grid of the intermediate amplifier tube 12 and anV equal amount passing a non-inductive resistor 22 and a condenser 23 to the intermediate amplifier tube 13. The current from the second conductor, connected to point 16, passes through a non-inductive resister 24 to the intermediate amplifier rtube 14. The values of the non-inductive resistor 20, the inductor 21, the non-inductive vresistor 22 and the condenser 23 are so chosen that the voltage applied to the input circuits of the intermediate amplifiers 12 and 13 are equal in magnitude and displaced by 120 degrees in time-phase from each other. Moreover, the voltage applied to the input'circuit of intermediate amplifier 12 lags the voltage between point 19 and ground by degrees and the voltage applied to the amplifier 13 leads the voltage between points 19 and ground by 60 degrees. The value of resistor v24 is so chosen that the voltage applied to the intermediate amplifier 14 is equal in magnitude to the Vvoltages applied to the amplifiers 12 and 13. Since the time-phase displacement between points 16 andv 19 iseXactly 180 degrees, it is evident that the voltages appliedv to the three intermediate amplifiers are respectively 120 degrees apart in time-phase. As will 'be eX- plained below, thetim'e-phase displacement between'the voltages applied to the grids of the three intermediate amplifying tubes must remain constant to prevent a shifting of the beacon courses in space. A Variation of the grid to filament tube impedances would tend .l I y After passingv to cause such a displacement. The resistances 25 (having values of 7500 ohms) are connected in parallel with the grid to filament impedances to minimize such variation. T.Vith this arrangement, a 20 per cent change in the grid to filament impedance of any tube results in but a 2 degree variation in the time-phase displacement.. Similarly, a change in the oscillator frequency of 2 kc results in a 0.2 degree time-phase variation. These are well within the permissible limits.

The output of tube 12 is modulated by means of a -cycle source of constant frequency supplied by the transformer 26 which is connected to a suitable source of alternating current supply.. The modulated radio frequency output of tube 12 passes throughra condenser 27 to the grid of a power amplifier tube 28. The amplified modulated high frequency current then passes through va condenser 29 and is transferred to'antennas 30 and 31 through the inductive Vcoupling between a stator 32 and the rotors 33 and 34.

Y By a similar series of transformation, the output vof the intermediate amplifier tube 13 is modulated by means of an 86.7 -cycle source of constant frequency supplied by a transformer 35 which is connected to a suitable source of alternating current supply. The modulated radio-frequency output then passes through a condenser 36 to a power amplifier tube 37, a condenser 38, and is transferred to the antennas 30 and 31 through the inductive coupling between a stator 39 and the rotors 33 and 34. Likewise, the output of the intermediate amplifier tube 14 is modulated by means of a 108.3-cycle source of constant frequency vsupplied by a transformer 40 which is connected to a suitable source of alternating current supply.v The modulated radio-frequency output then .passes through-a condenser 41, a power ampliiier tube 42, a condenser 43 and is transferredto'the antennas 30 and 31 through the inductive coupling between th-e stator 44 and the rotors 33 and 34.` The loop antennas 30 and 31 are tunedV to the master oscillator frequency by means of the condensers 45 and 46,V respectively. Proper grid bias is supplied to the intermediate amplifier tubes by means of a 220 volt direct current generator, (not shown) through radio-frequency chokes 47 and non-inductive resistors 48.

It is to be noted that although we used only one combination of modulating frequencies in the description of the preferred circuit, it isunderstood that any other suitable combination maybe employed.

The theory of operation of the transmitting circuit arrangement describedin Figure 1 may now be considered.l The modulated voltages applied to the three'stator coils 32, 39 and 44 are displaced by 120 degrees in time-phase. It is to be noted that intercoupling between stator windings does not exist since the stators are excited but one at a time owingV to this 120 degrees time-phase displacement. Each stator, acting in conjunction with the two crossed rotor coils and the two crossed loop antennas, sets up a system which is electrically equivalent to a single loop antenna. For zero rotor setting, the plane of this phantom antenna coincides with the plane of the stator coil considered. Since there are three stator windings, 'normally disposed at 120 degreesto each other,

three such phantom antennas (also crossed at 120 degrees) exist, each phantom antenna carrying current of the same radio-frequency, but modulated to a different low frequency. The carriers in the three phantom antennas being 120 degrees out of phase, both in time and in space, a revolving field is set up, the resultant carrier space pattern being a reolving iigure-of-eight of constant magnitu e.

The beacon space pattern obtained when using radio-frequency switching is shown in Figure 3, which consists of three figure-ofeight side band characteristics and a circular carrier 49. 5() indicates the iigure-of-eight side band characteristic from the stator 32 modulated at cycles, 51 indicates a similar characteristic from the stator 44 modulated at 108.3 cycles, and 52 indicates a similar characteristic from the stator 39 modulated Vat 86.7 cycles. The carrier is here represented as circular, this circle being the locus of successive maxima of the rotating figureof-eight actually produced.

The corresponding polar pattern assumingV square-law detection is shown in Figure 4, in which 53 shows the igure-of-eight reed amplitude characteristic due to the (S5-cycle modulation. 54 and 55 show similar characteristics due to the carrier frequencies modulated at 86.7 and 108.3 cycles, respectivel The courses lie along the lines LO, XO, T ZO, etc. Twelve courses are obtained, normally placed 30 degrees from one another.

quency of magnitude proportional to E0 El. y

In the case of radiovfrequency switching, the carrier which beats with each set of side bands, say F11, is 1.5 E0 as is evident from Figure 3. Consequently the resultant audio l frequency signal received is 1.5 EO'X El.

rIhe patterns of Figures 3 and 4 are for the special case when vthe three stator windings are exactly 120 deg. apart in space phase and the three voltages applied to these stators exactly 120 deg. apart in time phase. As will be observed,thef'carrier 'comprises a figureof-eight. revolving in spaceV at the carrierfrequency rate. The curve representing the carrier in Figure Sis inreality the locus in space of successive maxima of the rotating ligure. .s

It should be noted that each set of -side bands transmitted by one amplifier branch beats: with its own carrier and also with the in-phase components of the other two carriers of the system.

A departure of the three carrier voltages from exact 12C-deg. time-phase displacement results in a shifting of the beacon courses said master oscillator into a three phase radio frequency supply, means for using each phase of said three phase source for supplying carrier power to a particular one of said amplifier branches, a means of modulating the carrier wave in each of said branches to a low Vfrequency differing for each branch, a di- 2. In a directive radio beacon, the combination with a master oscillator, of three amplifying branches, means for converting a single phase radio frequency supply from said master oscillator into a three phase radio frequency supply, means for using each phase of said three phase source for supplying carrier power to a particular one of said amplifier branches, a means of modulating the carrier wave in each of said branches of a low frequency diifering for each branch, a directive antenna system comprising two directive antennas crossed at right angles to each other, means for transferring the modulated waves in succession from each of said three ampliiier branches to said kdirective antenna system whereby said three modulated waves are transmitted in predetermined directions to provide aV multi-course beacon space pattern, and means for modifying the resultant space pattern whereby the directions of anumber of beacon courses may be changed to align them with aplurality of airway routes converging on a Vradio beacon station.

In testimony whereof we ax our signatures. Y

-. HARRY DIAMOND.

FRANK G. KEAR. 

